In the computer industry, hard disk data storage elements or memory are generally made from aluminum or an aluminum alloy. Through a variety of processes, the aluminum is treated or otherwise coated and passivated so that it may act as a repository for information which is electronically written onto the disk. To ensure efficient and accurate data processing, hard disk components should be smooth or have an ability to be super finished to near atomic smoothness.
Hard disk memory components have certain properties or characteristics which make them commercially valuable products. One important parameter of concern for hard disk drives is increased processing speed. To increase processing speed, various drive design criteria have been modified. For example, the fly height of the disk head has been reduced, reducing the travel distance between the head and the disk. In turn, this gives higher bit density which reduces the processing time.
However, reducing fly height dictates that disk smoothness must increase as a matter of necessity. Hard drive disks preferably should have an ability to be polished to a high smoothness and to resist defects from operation such as holes, pits, digs, and scratches or mounds.
Another way to increase processing speed is to increase the speed at which disks rotate. However, higher disk spin rates (10,000 rpm or greater) can produce disk flutter or vibration as the disk works through operations of stopping, starting, varying speed and effecting actuator travel. Even at constant speed, disk flutter may result from turbulent air flow within the disk compartment or harmonic vibrations from the motor. Airflow is generally regarded as the primary cause of disk vibration.
The conventional material used in this fabrication has traditionally been aluminum or an aluminum magnesium alloy. Coating this alloy with a nickel plate provides a hard exterior surface which allows the disk to be polished and super finished. This type of disk is more easily finished. However, the relative flexibility of the alloys makes this type of disk more susceptible to environmental forces which create disk flutter and vibration.
One alternative to aluminum substrates for hard disks is the use of composite materials. However, these materials are not the easiest to finish. Previously, some attempts have been made to use materials which have properties of higher stiffness and smoothness.
For example, Japanese patent 4280817 discloses method for forming a thin zirconia film on a glass substrate. Zirconium n-propoxide, acetic acid and water are reacted to form a zirconia precipitate precursor gel, mixed with acetic acid and n-butanol, heated to 60.degree. C., coated and sintered onto the glass. The coated glass is thermally treated at 500.degree. C. to form cubic zirconia.
Vong, U.S. Pat. No. 4,397,671, discloses a method for forming a metal oxide film on the surface of a heated glass substrate by forming a powder from an organic based metal salt which is heat decomposable, such as metal acetyl acetonates.
Plumat et al., U.S. Pat. No. 3,850,665, disclose forming a metal oxide coating on a vitreous or nonvitreous substrate by applying to the substrate a composition comprising an acetyl acetonate coprecipitate of two or more metals. The substrate and composition are simultaneously or subsequently heated to convert the coprecipitate to a metal oxide coating.
Klinedinst, U.S. Pat. No. 5,118,539, discloses a method for coating titanium dioxide onto surfaces such as those comprising zinc sulfide or phosphorous to provide for any number of enhanced properties including chemical resistance to absorbency, as well as the filtering or reflection of electromagnetic radiation.
Further, Schultze et al., U.S. Pat. No. 5,043,182, discloses a method for producing ceramic metal composite materials through the application of ceramics onto a substrate. Subsequently, molten metal is infiltrated into the pores of the ceramic material. Bradstreet et al., U.S. Pat. No. 2,763,559, discloses a coating method for use in the application of refractory metal oxide films onto metal parts which are subjected to high temperature.
Composites provide disks of superior hardness and stiffness when compared to aluminum disks. However, composites are often difficult to coat and super finish. Specifically, composites are difficult to polish without giving rise to other physical defects during the polishing cycle. Because of hardness of certain composites, finishing cycles are very long and the disks begin to adopt certain characteristics which are undesirable such as edge roll off.
As a result, there is a need for disks of superior stiffness and hardness which resist defects, provide a smooth substrate surface, (to atomic smoothness), are relatively thin, and have low mass.